â–¡ Jin Qiusheng, the Fu'an Hydropower Management Office of Fu'an City, Fujian Province, has developed and applied vacuum circuit breakers. The actual use proves that it has obvious advantages over the oil-less circuit breakers: it has a large breaking capacity and extremely high dielectric recovery speed, and its volume is small. Light weight, short stroke, low energy consumption, low contact pressure, low breaking and closing vibration, low noise during operation, no explosion hazard, no pollution, simple maintenance and long service life. Because the contacts are in a vacuum, they are not affected by external dampness, dust, harmful gases and the atmosphere. Therefore, vacuum circuit breakers are widely used in power systems and power sectors in various fields, and will have the potential to replace oil-less circuit breakers.

However, the price of the vacuum circuit breaker is relatively high, and the creepage ratio of the outer insulation is small, and the operating overvoltage is easily generated when the current is broken.

Mechanism of Operation Overcurrent 5 A serious problem in the use of vacuum circuit breakers is that they are prone to operating overvoltages. But this is not terrible, as long as some measures are taken technically, this operation overvoltage can be suppressed.

The operating overvoltage of the vacuum circuit breaker includes the interception overvoltage, the three-phase overvoltage and the re-ignition overvoltage.

Cut off over voltage. It means that before the current is cut off, the current has not been abruptly interrupted by zero. After the current is cut off, the inductance and capacitance in the circuit will be oscillated at high frequency. The frequency of the 篼 is superimposed with the power frequency. This part of the electromagnetic will cause the arc to not extinguish, and the t is sharp. .

It is energy-saving to determine the transformer capacity based on the principle of minimum operating loss, but it is not the most economical. Only the transformer determined according to the total cost of ownership method is the most economical. This gives us a new concept and a new method. When determining the transformer capacity or determining the number of transformers, we must determine the minimum total cost of ownership of the transformer to ensure that the selected transformer has the best overall benefits. Qi.

(1) When determining the capacity of the enterprise jade transformer, in addition to technically meeting the requirements, it is necessary to carry out comprehensive economic comparison. The transformer capacity determined by the total cost of ownership method is the most economical, and it is worthy of pushing three-phase asynchronous overvoltage. . That is, tripping or closing of three phases in different periods is more serious when tripping. If the first phase is broken, abnormal reignition occurs, thereby causing the transient high-frequency current to be coupled to the second and third phases through phase-to-phase mutual inductance and capacitance, and superimposed with the original power frequency current on the second and third phases. A high frequency overvoltage is formed. Due to the strong arc-extinguishing ability of the vacuum circuit breaker, the two-phase arc is forcibly cut off.

Re-ignition overvoltage. Refers to the high-frequency re-ignition over-voltage, which is often caused by the natural zero-crossing of the power-frequency current when the vacuum circuit breaker contacts are separated. The arc-extinguishing is formed under this condition, and no over-current is present at this time. However, due to the small opening distance of the contacts, re-ignition may occur under the action of the recovery voltage. If reignition occurs, a reignition overvoltage is generated, and the overvoltage amplitude increases with the number of reignitions, and the steepness is also large.

The hazard vacuum circuit breaker is easy to generate operating overvoltage when it is turned off, and its overvoltage maximum can reach 4.3 times of the phase voltage, which has a destructive effect on the insulation of electrical equipment. It is easy to cause the motor stator winding or the power transformer primary winding burned by its control operation, resulting in economic loss. If effective measures can be taken, the overvoltage can be suppressed.

Measures to prevent over-voltage operation To prevent over-voltage operation, first of all, a good method from vacuum.

When determining the capacity of the main transformer, it is necessary to distinguish the economic load of the transformer and the concept of economic operation of the transformer. They are not equivalent and sometimes vary greatly. The above is a very ambiguous example. The transformer selected according to the economic load of the transformer is 12500kVA, and the transformer selected according to the economic operation of the transformer is 20000kVA. A problem can be found from the calculation of the soil surface, when the main transformer is in economy under a certain load. During operation (when transformer loss is minimal), it is not the most comprehensive economy. The reason is due to the current national electricity price billing policy. It is recommended to reform the internal structure and processing technology of the current two-unit electricity price circuit breaker.

In the manufacturing plant, the pressure of the saturated steam of the contact is increased to reduce the level of interception. In order to prevent the insulation strength from decreasing, the contact should be made of a material having a low boiling point and a small thermal conductivity. From the maintenance point of view, the newly-invested vacuum circuit breaker is subjected to the "old refining" process, and the operating mechanism opening speed is appropriately lowered.

Additional protection against overvoltages is: shunt capacitors on inductive loads such as motors or transformers to reduce the load wave impedance, thereby reducing the crossover overvoltage, not only reducing the magnitude of the overvoltage, but also reducing the leading edge of the overvoltage waveform. Steepness.

This type of protection method is cumbersome, bulky, costly, and not easy to install. However, it is preferable to use this method for an electric device that frequently starts with a large load.

The parallel-connected zinc oxide (Zn0) arrester at the load end can be oxidized to prevent overvoltage. The zinc surge arrester acts as a non-linear resistance absorber in parallel with the electrical equipment. The utility model has the advantages of low residual pressure, fast reaction time, small volume, light weight and convenient installation.

The main parameters of the arrester are nominal voltage, residual voltage ratio and flow rate.

The charging method, the basic electricity fee is abolished, and a electricity price billing system is adopted to appropriately increase the electricity bill per degree to compensate for the partial electricity bill that is reduced by canceling the basic electricity bill, so that the electricity bill is not related to the transformer capacity, so that the enterprise runs the transformer with the least loss. The transformer capacity determined by the principle can make the transformer run the most economical, and it can combine the best economy and achieve the purpose of energy saving.

This paper discusses a single transformer as an example. Multiple transformers can also be used to analyze the comprehensive economic benefits according to the above principles, and run the transformer well from energy saving.

(Electrical Age

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